hey, so i just got a graphing calculator because i just started pre-calc/trig, and i dont know how to use it. could you help me with some basic functions?

for example, i want to check these answers graphically:

equation1: y=12-4x

answer1: x=3

equation2: y=x^2-2.5x-6

answer2: x=-1.5,4

i dont know squat about the calculator yet, so please be patient and tell me *exactly* what to do.